The invention relates to a device and a method for detecting a fault in a measurement device comprising a resonator and means for measuring a resonant frequency of the resonator. The measurement device comprises, for example, a fluid pressure sensor. The invention is particularly useful in aeronautics, in which pressure measurements are of paramount importance for controlling the flight of an aircraft. This is because the altitude of a flight level required for an aircraft is determined by the static pressure of the air surrounding the aircraft. Moreover, since air traffic is increasing, traffic control authorities seek to reduce the difference between two neighboring flight levels. It is essential to detect a defect in a pressure sensor in order to guarantee air traffic safety.
The invention may also be employed for other devices using a resonator, such as for example in an accelerometer, as described in French Patent Application FR 2 848 298, a gyro, as described in French Patent Application FR 2 834 055, or else in a timebase. The rest of the description will be given solely with reference to an air pressure sensor, without of course limiting the invention.
To measure the pressure of the ambient air, it is common practice to use pressure sensors comprising a chamber maintained at a reference pressure, generally close to vacuum. An example of this type of sensor is described in French Patent Application FR 2 687 783. The pressure sensor measures a pressure difference between the chamber and the air. The guarantee of the precision in the pressure measurement essentially depends on maintaining the vacuum within the chamber over the lifetime of a sensor, or at the very least between two calibrations of the pressure sensor. Several effects may degrade the vacuum within the chamber, such as in particular leaks that may occur at the joints of various components of the walls of the chamber or else outgassing from the walls or from the components located in the chamber.
The pressure sensor described in French Patent Application FR 2 687 783 includes a resonator, one end of which is exposed to a force that depends on the pressure difference between the inside of the chamber and the ambient air. The principle of the pressure measurement consists in measuring the resonant frequency of the resonator.
Moreover, it has been shown that, at constant air pressure, the ambient temperature has an influence on the resonant frequency. It is possible to add a temperature sensor to the pressure sensor. During a calibration phase, a function combining the measured temperature and the resonant frequency is established in order to determine the pressure. This function may be established empirically. This correction does not take into account any modification of the pressure in the chamber. At the present time, only a recalibration of the pressure measurement device allows such a modification to be determined.